Extrusion



Nov. 24, 1953 IIIIIIIIIII IIII IIIIHIIII'II Nov. 24, 1953 H. M. GERSMAN EXTRUSION 2 Sheets-Sheet 2 Filed June 5, 1946 )NVE/vio@ HARVEY M GEMMA/v Patented Nov. 24, 1953 EXQRUSIQNJ Harvey M; Gersman, New York, N. Ya, assignono ones-.tenth to George Jordan, Montclair, and one-.tenta to Aeolnh Gf Wieren), Einser nnnli'eatiennne, 53,1946, Seria! NQ-,lirliSl (C1. atterra,

l2. Claims. 14

The present invention, relates to extrusion off metals orother materials in a plastic state, such as metals renderedplastic by heating, and is more particularly directed to what may be ter-med direct extrusion, that is, the directfrnovement of the metal of a billet through an orifice in one end of a container by means of a moving ram acting against the other end of the billet to compress it and cause it to flow through an orifice of the container.

The present invention is primarily directed to the extrusion of such metals as those of the iron group,v copper and copper-eontainingVv alloys or light alloygroup, such as aluminum and magnesiurn, since Il have found that the rsame general principles may be applied to the extrusion of all of these materials without the disadvantages and the objections which have heretofore been found, particularly in the extrusion of the higher melting point metals. The present methods properly joined to the lowerl curve'produces'the causedextreznely rapid die weaj and poor products as well as generally high production toste.

To the accomplishment of the foregoing and related ends, said invention, then,` consists of the methods and apparatus hereinafter fully de scribed and particularly pointed out in the clairnsgcertain of the annexed drawings as specified loelow and the accompanying description setting forth in detail one approved method' and apparatus ofcarrying out the invention, such disclosed method and. apparatus ,hw/ever,V eenettntne but One 0f the various Ways in which the nrnenie of the invention may be used. A

In Said annexed drawings:

Fie- 1 Yis a diaerannnatiei fraementary2 vertical mid-Sectional elevational View er an ertrnen rn'linder,Y ram and. die whien innetrates eertan phenomena that are inherent in eenventienal erf trusion operations;

Fie. 2 is an enlarged fragmentary View eerref spending to Fie. 1, further illustrating Qertain disadvantages o f the prior art;

Fe- 2A Shows a result Sometimes eeeurrne from the eonditionsmostrate@ in rig.

Fig. 3 is a partial mid-sectional"elevatippnval View 0f extrusion apparatus embodying the vreeent invention;

Fis, 4 1S a diagrammatic axial eeetienal eleva: tion of one-half of a billet illustrating one me of determining the ieed enrve or the'natural of new of the metal ef the billet ,freni the eine wall of the container toward the orifice under the action of the ram, the curve being egtended from the center line of the billet;

Fig. 5 is an axial sectional elevation of one- I and also the`curve` required in the orice por.

tion of1 the die which 'is joined to the' used portion o f the freedcurvef;

Fier. '7 is the complete punch test curve of Eig. 6 for the full width of the punch, or which only- Qne-half is shown in Fig.. '52 reduced to the dise tance between the edge of the r-ice and the edge ofthe side wall ot the billet for which the complete die curve is to hefound', and also shows therealoove the feed cu-rve or F-igf. 4, which when 1 Wall of the containerto the edgeof the orice.

In the extrusion of metals of the types re'- ferifed` to, diiicultyhasy always heenA experiencedfrom certain factors which include very severeabrasion on the edge of: the or-iiice die and very considerable power and temperature require'- ments. A third and, in some cases, still 'more important factor has heen the creation ofi piping in the extruded product. Extrusion pipe consists of an outer layer on the extruded product formed of metal caused to flow or eXtr-ide under iinproper conditions and at a different speed than the core orcentr-al metall ,This pipe' increases 1n diameter as the extrusion progresses." Where seen piping occurs, the preque't'must b iria; shines down t@ up' minirrnum'eimetr Ordesa core metal if the product isy to'b emplyedwhre any considerable 4degree f strength 'is 'required or where it is to be further machinedl a's the outer layer, that is, the'piping, 'causs' 'eli"atter`A ing oft machine tools aridprevents ever and uniform machining; The metal' altthe junetreof pipe and core metal containsV scaleinsome ss and the bond is only aniehanical 'onl "nl Y' A All of these diiculties'and 'other' extrusion difficulties arise from improper 'flow` ci thez'rnat' mi or me billet t@ gpd'throughn ii uii'r the innuence of the ram." Whiivaris ns of orifices have been suggested 'to' improve the flow, none have produced" uniform or straight; line flow through theI orice'wit-out anyturav bulence around the edges of the orifice. Nor have they eliminated the factors which have caused the action Within the billet which is detrimental to the smooth progressive iiow of all the metal to and through the orifice so that all the metal may issue with uniform single directional flow parallel to the axis of the part being extruded.

`So little beneficial effet has been secured from many of the various dies heretofore suggested for extrusion that the greater part of extrusion of all of the metals named hereinbefore has heretofore been carried out through an orice which is merely a circular hole (or a hole shaped in cross-section to produce the part required) in a flat end plate of the container, there being no `speciallycontoured die as suchof any kind.

It will, of course, be understood that when a billet of plastic metal or metal heated to plasticity is acted upon by a ram and is thereby being forced toward the end of the container and through an orifice formed in an end plate thereof, the metal of the billet will naturally move along some angular line from the side walls of the container toward the orice. The metal will naturally not turn a right angle and will therefore not proceed directly along the side walls to the end of the container, then turn inwardly, moving across the end wall of the container and then again turn at a right angle and move out through the orifice. This is so obvious that it hardly needs to be stated. It is equally obvious that the metal along the side Wall will move along some inclined or curved path starting at some distance on the side wall from the end wall and toward the orifice through which the metal may be extruded The result of such action of the metal is, of course, to shear the main portion of the billet away from that portion resting in the corners of the container, thus leaving this more slowly moving and compacted metal in the corner portions of the die. This is obviously, however, an extremely wasteful procedure and cannot help but produce irregular flow of metal to and through the orifice. Nevertheless it has not heretofore been determined what path of ow the metal actually takes as a result of this shearing action. Therefore, it has not been possible to devise a die to conform to the natural flow of the material and to cause it to flow smoothly and uniformly to and through the oriiice. The shearing action within the billet also requires a considerable pressure and considerable additional heat so that the billet is sufficiently plastic to permit this action to occur.

In a conventional die such as that referred to above, when the ram, of course, moves forward a given distance it will displace an equal volume of metal. This volume of displaced metal which is extruded through the orice comes mainly from the central and obviously more rapidly flowing central portion of the billet. The relatively inert metal in the corners of the container which is acting as if it were a die due to the mentioned shearing action is moving much more slowly toward the orice and is being crowded radially inwardly and over the edge of the orice. Progressive movement of the ram increases the movement inward of this trapped corner metal and as the ram continues to move toward the orifice the opening in the orifice available for the faster moving central billet metal is progressively reduced, the balance of the orifice opening being filled by the ow from the trapped inert corner metal. This produces the increased piping or outer layer on the extruded product and this metal is neither straight 4 fbered metal with the fibers parallel to the axis of the extruded part nor is the bond between this extruded corner metal, and the central portion of the billet metal a true bond.

A further harmful effect resulting from the aforesaid type of movement is a checking or tearing of the surface of the extruded part, which tearing at times extends almost to the center line of the part itself. This is caused by the difference in the emerging speed between the core metal and the inert corner metal carried along on the outside. The condition of the extruded metal from a temperature standpoint, brittleness, etc., together with the overall rate of speed, will cause the extruded material to crack, which cracking in some instances appears simply as surface checking, whereas in other instances it will cause tears extending well into or through the extruded part.

This necessary elongation of the thin iilm of inert metal carried along into the orifice initially at a slower speed than the moving metal by reason of the differential in their speeds, appears to be self-evident when once pointed out, but apparently never been recognized as the cause of severe loss in products of extrusion and is found in extrusion of any of the metals named where the conditions are those described above. The extent of this surface checking and tearing action is greatly dependent upon the overall emergent speed of the extruded part. The faster the speed the more the ripping or tearing action upon the stretched material on the outside of the part. The tensile strength of the metal decreases with increase in temperature and at the higher extrusion temperatures the tensile strength is so low that tearing due to the action described is more common. To avoid this heretofore, extrusion of many products had to be carried out at temperatures and speeds which are commercially undesirable.

The result of operating at such higher temperatures and pressures is, particularly in the case of metals of the ferrous group, that the pressures exerted against the die are higher than the available strength in die steels at that temperature and as regards pressures requires extremely heavy and expensive presses, which naturally reduces the otherwise very great savings of extruu sion over other methods of metal reduction. lt is also well known that to heat billets to the higher extrusion temperatures thus necessary, increases the costs disproportionately. In spite of all of the above objections in the existing methods and apparatus for extrusion, it is still, of course, wide- -ly practiced with the softer and lower melting point metals. This is true because of the very much lesser abrasive effect of such metals on the die, the lower temperatures required and the reduced structural strength required in `1y of the products, such for example, in architectural shapes, angles, moldings and the like.

From a great many of experiments from which I have determined, and which have been demonstrated, the objections and the defects in isting methods and apparatus for extrusion, i' have found that extrusion can best be practiced only under conditions where the metal is allowed and confined so that it follows its own natural paths of flow through the orifice. The die employed must conform to these natural flow paths in order to prevent turbulence in the metal, excessive pressures at different points against the die face, and internal shearing of the metal with the resultant disadvantages. I have also found it possible to determine for any given metal the precise paths: which, in tumv determina the.

die curve and and; althoughl these vary' for diherent metals', the variance is not as large as might be expected and. can. be accurately determined for any given metal. by a simple and inexpensive' preliminary test made upon the metal in question.I When this is done; as will be explained hereinafter, I.. am able to produce a die which will coni-lne the m'etal to the proper' flow paths to and through: the orifice; and thereby greatly to reduce the pressure: and temperature required, minimize or entirely avoid. all of. the objectionable flow features which have hereto-- fore characterized extrusion and, to produce continuously uniform, substantially parallel'. grained or nbered products.

It is evident that a proper die outlining and confining the flow of that portion. or the billet which. provides the core metal of the extruded part must be comprised. of` two sections, namely the proper contour of the shear line, since this shear line is formed as the resultv of thel flow path taken by the properly flowing portion of the billet, and second, the orihce curvature as this properly flowing portion approaches and flows into the oriiice. These two portions oi the proper flow line or die line cany be characterized as, rst, the feedv curve and, second, the orifice curve. Further experimentation with. varioussized orifices showed conclusively that the feed curve followed substantially the same contour, regardless of the oriiicel size, up to the point where the orice curve began, and showed further that the oriiice curve varied with the size' of the orifice opening.

It became evident that the formation of the n feed curve or the approach from the side wall to the oriiice sector wasl the result of streamline or viscous flow within the billet itself. Such viscous iiow is the result of varying speeds of i flow within the billet itself. As a portion of the billet is displaced through the rice as the result of a forward movement or the ram, other portions of the billet move to replace this material and continue onward to flow in turn through the oriiice. Such flow to andv through the orice reaches its maximum speed at the center line and gradually decreases as the side wall is approached.

To lay out a die curve coinciding with this viscous flow for each material to be used, it. is necessary to know the factors which govern the formation of this curve or the factors which govern the viscous flow within the billet itself. One of these governing factors is the angle of internal iiow of each material. in question.

By experiments I discovered that under standard conditions, the angle at whichv this viscous now curve reached the center line of the billet was the same as the angle at which this curve began at the side wall of the container, and thatA this angle coincided with the angle of internal now.

This discovery made it appear probable that I' could use a simple and standard method for laying out this Viscous flow curve for any given material and this was later found to be correct. This method is as follows: The billet is theoretically divided into portions of equal con centric volumes, usually to 20. The begin-v ning angle, or the angle at the side wall, as well as the last angle, approaching the center, being the same, and since the entire curve is contained within a 90 angle, it is then only necessary to determine the angular diierential difierential` can. be determined by the standard formula for' arr arithmetic progression.

(Il gamma=phi-f-(n-l)" beta wherei gamma is thev slope.. expressed. degrees or. radi-ansi of the flow curve at. any point thereof,

phi is'` the beginning angle.. n. the number of equal.:volumesl encountered. in passing` from the container sidewall to any point or the new curve, beta the angular increment added toA alpha in: passing from. one volume to the` next..v

The nal value of gamma is obviously 1r/2.- alpha where alphay is the last angle at which the curve intersectsk thev billet axis and as measured with reference to a line perpendicular tothe axis of the billet. Thus ire-cm1@ (2l) N T-I where N'T is the total number of volumes into which the billethas been theoretically divided.. And since, as above stated, alphazphi, then 1r/2- 2f alpha Since the billet is of constant height the above formulas apply to a transverse section thereof which is theoretically divided into concentric portions of equal area, in which case Nr would be the total number of such areas and N the number of such areas disposed between the billet axis'and. an ordinate paralleling the axis from any point on the flow curve. Therefore, to properly construct the viscous ilow curvey or the feed line for any given material, it is necessary to know the angle of internal flow for that particular material.

Froml a number of tests I discovered that the action of the end face of the container, or in other words the die section against the billet was that of a punch. From this it followed that the orifice curve or the path which the metal would follow in flowing into and through the orifice was similar to the path which that metal. would follow in flowing aroundv the edge of a punch whose diameter was equal to the distance from the oriiice edge of the side wall. Therefore, to properly outline the oriiice curve, such a flow path around the edge of a properly dimensioned punch must be secured.

It was found that both needed factors, namely the angle of internal flow and the path around the edge of a punch, could be determined by means of one test. A billet of selected material at extruding temperature is confined within a die open at one end. A punch of lesser diameter than the billet is forced into the billet at that open end, the punch being heated to avoid creating a chill in the metal. The displaced metal flows from the center line of the punch in each direction towards the side of the punch and eventually around and past the endV or edge of the punch.- The metal adjacent to the face of the punch and outlined by this iiow is static, regardless of the distance of punch penetration, and remains so unless deformed by other forces.

Analyses of the contour of this static zone adjacent to the face of the punch shows that for varying distances on either side of the centerline, the displaced material hows on a true radius or arc ofi a circle. This true radius becomes a beta= beta parabola as it continues to ow to and around the edge of the punch. This parabolic portion provides the actual path which that particular type of material will follow in flowing around the edge of a punch of that diameter and therefore provides the elements required for establishing the orice curve for that material for any given diameter and for any given orice Width. The angle contained by a line drawn parallel to the face of the punch through the apex of flow at the center line of the punch and a line drawn between that apex and the juncture point between the true radius and the parabolic section provides the angle of internal flow for that particular material. This is the angle phi in the formula already given.

Using this angle of internal how in the Inanner previously described, I can thus establish the true and exact contour of streamline or viscous flow within the billet for any given diameter. This contour establishes the so-called feed line previously referred to and extends from the side Wall to the center line of the billet. With the orifice dimensions established, the distance from the oriiice edge to the side Wall becomes known. Using this distance as the diameter of the punch a properly proportioned outline of the static rone can be drawn, including the true radius portion and the parobolic section up to the edge of the punch. Joining this punch test curve to the feed line at a point of tangency establishes the complete die line for the tested material for a given diameter and given orice Width.

Referring now to the drawings, in Fig. 1 I have shown a standard container i provided with an end Wall 2, a die opening 3, a billet 4 in the process of being extruded therefrom and a ram 5. There is no die as such shown in this gure, the end Wall 2, of the container with its opening 3 actingas the die, and as a result, that portion of the billet in the corners 6 of the container has to act more or less as a die in conjunction with the orifice, the billet being sheared away from these corner portions or zones along a surface of revolution having roughly the conguraticn in axial section illustrated as single lines l, but which in practice are not only irregular but sometimes of considerable Width.

In such an extrusion, proper flow cannot be secured as there is constant shear between the moving center portion 8 and the relatively unmoving corner portions of the metal, with turbulence found in the flow along the boundaries l between the two portions; and also With the further result that metal from the corner portions E is gradually pushed and carried over to the edge of the orifice in increasing amounts as the extrusion progresses, producing, as is shown in Fig. 2, an exterior progressively thicker coating or pipe or" metal S which comes from the corner portions 5 and which is not truly bonded to the actual core IU. This pipe is also not good metal and sometimes contains foreign material and has to be removed down to the minimum diameter of true metal in the extruded product iD if the latter is to be used where strength is an important factor.

Still referring to Fig. 2, the core metal Il] approaches and is extruded through the orifice at a much higher rate of ilovv than the more or less inert corner material 6. As a result the outer layer or piping 9 of the extruded product is stretched compared to the core, often resulting in surface tearing, which in some instances appears simply as surface checking, but which in other instances Will extend Well into or entirely through the extruded part, in the manner illustrated at l I of Fig. 2A.

In Fig. 3 there is shown the same general type of extrusion apparatus as shown in Fig. 1, that is, it includes a container or cylinder |011, a ram Ha, a billet l2 and a die I4 leading to an orifice l5. The construction of the die must be such that all of the metal in the billet will follow the natural path of flow of the metal without turbulence, and in such a way that the metal will issue from the orifice in streamline condition, that is, with straight parallel bers of metal in the extruded product. The proper die to accomplish this purpose will now be described.

The contour of the die I4 is shown in its cornpleted form in Fig. 8, but the portions which go into the complete contour of the die are arrived at by first laying out the die in several portions as illustrated in Fig. '7, which portions are then joined in the manner which is shown in Fig. 8 to produce the completed die.

In Fig. 4 for instance I have shown one-half the billet l2 of Fig. 3, the center line of the billet being represented by the line Y-Y and the lower end of the billet by the line X-X- This billet is then theoretically divided into ten or more portions of equal volume concentrically arranged around the center line Y-Y of the billet as indicated by the lines i9 representing concentric cylinders or tubes, and a series of points are determined by the method already described hereinbefore with reference to formula l.

Through these a curve l 6 is drawn from the side wall or outer surface il of the billet to the axis or center line Y--Y thereof.

Thus with reference to the above formula in Fig. 4, alpha is the angular slope with reference to the :c axis, of the tangent at any point on curve 16. Phi is the beginning angle at which the billet metal shears away from the extrusion die sidewalls, n the number of portions i9 of equal volume, encountered in passing from the sidewall to any point on curve IS, and beta the angular increment added to alpha for each successive volume portion. Also in Fig. e, alpha is the last angle as measured with reference to the :c axis, or 1r/2-gamma as measured with reference to the y axis, While NT is the total number of equal volumes into which the billet is theoretically divided.

In order to derive curve i6, Fig. 4, as a continuous mathematical function of x and y, it is for convenience rewritten With reference to the billet axis, y, as follows:

(4) delta=alpha+ (71*1) beta Assume now that the total number of equal volume portions NT into Which the billet is theoretically divided is allowed to become extremely great, approaching infinity, in consequence of which the radial thickness of each volume portion I9, Will become correspondingly small, equaling, at the limit, the diiferential thickness dr. As a result distance along the :L axis to any point in curve i6, Will equal n dw, so that (5) 1z=:c/d:c

Also each of the volumes I9 will become equal to (6) 21r.r.da:.h=K

where h is the 4billet height and K a constant,

one said volume to the next, and phi the angle at which said curve diverges from said sidewalls.

2. In an extrusion die, a tubular member hav-` ing inner sidewalls which converge at one end thereof toward an orice along a concave feed surface, comprising, in axial section, a continuous curve constituted of an arithmetic progression of terms representing equal concentric volumes to be displaced during extrusion, said curve corresponding substantially to the formula wherein n is the number of such equal Volumes disposed between the die sidewalls and any point on said curve, gamma is the angular slope of said curve at any point thereof, beta the angular increment by which said slope is changed in passing from one said volume to the next, and phi the angle at which said curve diverges from said sidewalls, and wherein phi has a magnitude substantially equal to the minimum angle of internal fiow of a metal to be extruded.

3. An extrusion die consisting of a tubular member the inner sidewalls of which converge at one end thereof along a concavely curved feed surface toward an orifice formed in said end of said die, said feed surface terminating adjacent said orice in a convexly curved orifice portion tangential thereto and extending thence to said orifice, said feed surface comprising in axial section a continuous curve constituted of an arith metic progression of terms representing equal concentric volumes to be displaced during ex trusion, said curve corresponding substantially to the formula wherein 11, is the number of such equal volumes disposed between the die sidewalls and any point in said curve, gamma is the angular slope of curve at any point thereof, beta the constant angular increment by which said slope is changed in passing from one volume to the next, and phi the angle at which said curve diverges from said sidewalls of said die.

ll. A11 extrusion die consisting of a tubular member the inner sidewalls of which converge at one end thereof along a concavely curved feed surface toward an orifice formed in said end of said die, said feed surface terminating adjacent said orifice in a convexly curved orifice portion tangential thereto and extending thence to said orifice, said feed surface comprising in axial section a continuous curve constituted of an arithmetic progression of terms representing equal concentric volumes to be displaced during extrusion, said curve corresponding substantially to the formula gamma=phi+ (1t-l) beta wherein n is the number of such equal volumes disposed between the die sidewalls and any point in said curve, gamma is the angular slope of said curve at any point thereof, beta the constant angular increment by which said slope is changed in passing from one volume to the next, and phi the angle at which said curve diverges from said sidewalls of said die, said orifice portion having in axial section a substantially parabolic curvature extending tangentially to said orifice.

5. An extrusion die consisting of a tubular member the inner sidewalls of which converge at one end thereof along a concavely curved feed surfacetoward an orifice formed in said end of said die, said feed surface terminating adjacent said orifice in a convexly curved orifice portion tangential thereto and extending thence to said orifice, said feed surface comprising in axial section a continuous curve constituted of an arithmetic progression of terms representing equal concentric volumes to be displaced during extrusion, said curve corresponding substantially to the formula gamma=phi+ (1t-1) beta wherein n is the number of such equal volumes disposed between the die sidewalls and any point in said curve, gamma is the angular slope of said curve at any point thereof, beta the constant angular increment by which said slope is changed in passing from one volume to the next, and phi the angle at which said curve diverges from said sidewalls of said die, and wherein phi is substantially equal in magnitude to the minimum angle of inter-nal flow of a metal to be extruded, and wherein said orice portion conforms substantialhT to the flow path of said metal about the edge of a punch forced into said metal.

6. An extrusion die comprising, a tubular member the inner sidewalls of which converge at one end thereof along a concave feed surface to an orifice coaxial therewith, said feed surface in axial section conforming substantially to the formula dy/dx=tan (alpha-i- (ar/Z-phi-alpha) wherein the y axis is the axis of said die, and the (c axis intersects the same at a point where a projected continuation of said feed curve intersects said y axis, phi is the angle at which said feed curvey diverges from said sidewalls, alpha the angie between said feed curve continuation and sai-:l axis and X the ratio of any abscissa to said curve and the inner sidewall radius of said die at said axial section.

7. An extrusion die comprising, a tubular member having an inner sidewall portion of cylindrical configuration which converges at one end thereof along a concave feed surface of revolution in an orifice coaxial therewith, said feed surface in axial section conforming substantially to the formula dy/d:v=tan (alpha+ (fr/Z-phi-alpha) X2) wherein the y axis is the axis of said die, and the n: axis intersects the same at a point where a projected continuation of said feed curve intersects said y axis, phi is the angle at which said feed curve diverges from said sidewalls, alpha the angle between said feed curve continuation and said :n axis, and X the ratio of the abscissa to any point of said curve, and the inner sidewall radius of said cylindrical portion.

8. An extrusion die comprising, a tubular member the inner sidewalls of which converge at one end thereof along a concave feed surface to an orifice coaxial therewith, said feed surface in axial section conforming substantially to the formula wherein the y axis is the axis of said die, and the n: axis intersects the same at a point where a projected continuation of said feed curve intersects said y axis, phi is the angle at which said feed curve diverges from said sidewalls, alpha the angle between said feed curve continuation and said .r axis, and X the ratio of any abscissa to said curve, and the inner sidewall radius of said axial section, and wherein at least one of the angles alpha and phi is substantially equal in magnitude to the minimum angle of internal iiow of a metal to be extruded.

9. An extrusion die comprising, a tubular member the inner sidewalls of which converge at one end thereof along a concave feed surface to an orifice coaxial therewith, said feed surface in axial section conforming substantially to the formula cly/da:=tan (alpha-l- (1r/2-phi-alpha) X2) wherein the y axis is the axis of said die, and the :c axis intersects the same at a point where a projected continuation of said feed curve intersects said y axis, phi is the angle at which said feed curve diverges from said sidewalls, alpha the angle between said feed curve continuation and said :r axis, X the ratio of the abscissa to any point o-f said curve, and the inner sidewall radius of said axial section, and wherein at least one of the angles alpha and phi is substantially equal in magnitude to the minimum angle of internal flow of a metal to be extruded, and wherein said feed surface extends to said orice along a convexly curved surface portion tangential thereto, said convexly curved feed surface conforming to the iiow path of said metal to be extruded, about the edge of a cylindrical punch forced axially into said metal.

10. An extrusion die comprising, a tubular member the inner sidewalls of which converge at one end thereof along a concave feed surface to an orice coaxial therewith, said feed surface in axial section conforming substantially to the formula dy/dr-tan (alpha+ (1r/2-phi-alpha) X2) wherein the y axis is the axis of said die, and the :v axis intersects the same at a point where aA projected continuation of said feed curve intersects said y axis, phi is the angle at which said feed curve diverges from said sidewalls, alpha the angle between said feed curve continuation and said a: axis, X the ratio of the abscissa to any point of said curve, and the inner sidewall radius of said axial section, and wherein at least one of the angles alpha and phi is substantially equal in magnitude to the minimum angle of internal flow of a metal to be extruded, and wherein said feed curve extends to said orifice along a convexly curved surface portion tangential thereto and of substantially parabolic configuration in axial section.

11. An extrusion die comprising, a tubular member the inner sidewalls of which converge at one end thereof along a concave feed surface to an orice coaxial therewith, said feed curve in axial section conformingto substantially the formula wherein the y axis is the axis of said die and the axis intersects the same at a point where a projected continuation of said feed curve intersects said y axis, alpha is the angle between said projected continuation and said m axis and also the angle at which said feed surface diverges from said sidewalls, and X the ratio of an abscissa to any point of said curve, and the inner sidewall radius of said axial section, and wherein alpha is substantially equal in magnitude to the minimum angle of internal iiow of a metal to be extruded, and wherein said feed curve extends to said orifice along a convexly curved surface portion tangential thereto and of substantially parabolic configuration in said axial section.

12. The method of forming a tubular die for the non-turbulent extrusion of a preselected metal to be extruded through an orifice formed in one end of said die, which comprises, forcing a cylindrical punch axially into a block of said metal, and determining from the resulting static zone formed in said metal beneath said punch, the minimum angle of internal iiow of said metal and also the flow path of said metal about the embedded edge of said punch, imparting to the inner surface of said die a concave feed surface extending from the inner sidewalls thereof substantially to said orifice, said surface conforming in axial section substantially to the formula wherein the y axis is the axis of said die and the :c axis intersects the same at a point where a projected continuation of said feed curve inter# sects said y axis, alpha is the angle between said projected continuation and said :L axis and also the angle at which said feed surface diverges from said sidewalls, the magnitude of said angle alpha corresponding substantially to said minimum angle of internal flow of said metal, said feed curve extending to said orifice along a convexly curved surface portion tangential thereto and conforming substantially to the flow path of said metal about said punch.`

HARVEY M. GERSMAN.

References cited in the me of this patent UNITED sTATEs PATENTS Number Name Date 1,789,675 Elias Jan. 20, 1931 1,924,294 Shirk et al. Aug. 29, 1933 1,948,242 Schubarth Feb. 20, 1934 2,239,425 Jacobson Apr. 22, 1941 2,335,590 Gersman Nov. 30, 1943 2,341,749 Webb Feb. 15, 1944 FOREIGN PATENTS Number Country Date 516,653 France Apr. 23, 1921 

